Apart from its energy efficiency and low fabrication costs, LED technology offers a high degree of geometric adaptability when used in displays and light-emitting signs. Arrays of LEDs can be mounted on flexible substrates, such as a textile substrates. The array structure, which contains a plurality of small light-emitting bodies instead of larger incandescent or fluorescent light sources, provides an evenly distributed luminance. In order to achieve a comparable evenness using incandescent or fluorescent light sources, the display or sign must be given a considerable thickness.
LED technology has also been used for providing displays and signs of variable size and shape. One economically advantageous way of manufacturing such devices is to treat the LED array (when mounted on its substrate and possibly covered by diffuser layers and the like) as piece goods, furnished by the metre and capable of being cut to the desired size essentially without detriment to the function of the LEDs. Suitably, such arrays have distributed means for providing each LED with a driving current, either a separate unit for each LED or—more wiring-efficiently—one unit for every group of a fixed number of LEDs. The latter solution may not function properly if it is cut according to certain geometries, particularly geometries having an irregular contour or interior holes, as may be desired in connection with logotypes and the like.
FIG. 1 shows a cut-to-measure display in which each pixel 102 is controlled by a separate control means 101. The totality of the controllers are communicatively coupled to a main controller 105, which requires extensive horizontal and vertical wiring 104a, 104b. Clearly, each pixel inside the circular edge is connected to a control means. FIG. 2 shows an example of the other solution, wherein each control means 201 is connected to 16 pixels 202. Similarly to the device shown in FIG. 1, a main controller 205 controls the respective control means 201 via a plurality of connection leads 204. Near the circular edge are located a plurality of pixels 203, which are non-operable for lack of connection to their respective control means. This implies that the set of operable pixels will exhibit a different contour than the desired circular one; the resulting contour is substantially quadratic.
Co-pending application WO 2008/120132 discloses a cut-to-measure display device comprising LEDs organized in pixel groups. In the disclosed embodiments, each of the pixel groups comprises a controller connected to each LED in the group and adapted to provide it with a driving current. In WO 2008/120132, it is noted that the pixel groups may be provided with several controllers each, to make the display device more robust to cuts. This organization decreases the probability of pixels losing every connection to a controller, since this would correspond to all controllers in a pixel group being located on the same side of the edge (and outside the display device) after cutting.